Stripper mechanism for injection mold

Abstract

An injection-molding machine has a fixed and a movable outer platen bracketing a movable intermediate platen, the latter having a runner system conducted via an extensible or flexible conduit to a source of molten plastic material to be injected into cavities defined by respective pairs of mold portions supported by the three platens, the cavities being formed in part by cores carried on the outer mold portions. A stripper plate inserted between each pair of mold portions is articulated via a spring-loaded lost-motion link to a respective eccentric pin on a pinion which is rotatably mounted on the intermediate platen and meshes with a pair of racks respectively secured to the two outer platens; this linkage is duplicated on opposite sides of the mold. In an initial phase of a mold-opening stroke, the stripper plates move outwardly under spring pressure while remaining in contact with their respective outer mold portions whose cores still retain the freshly molded articles. When the limit of the lost-motion travel is reached, the stripper plates are slowly lifted off their adjoining mold portions to detach the molded articles from the cores.

We claim: 
     
       1. In an injection-molding machine having a plurality of relatively movable platens including a first platen carrying a first mold portion and a second platen carrying a second mold portion, said first mold portion being provided with a projecting core receivable in a mold-closed position in a recess of said second mold portion for defining therewith an injection cavity, the combination therewith of a stripper plate penetrated by said core sandwiched between said first and second mold portions in said mold-closed position and mechanism for detaching said stripper plate from both said mold portions upon displacement of said platens into a mold-open position to disengage a molded workpiece from said core, said mechanism comprising:   a rack secured to said first platen and extending past said second platen in said mold-closed position;   a pinion rotatably journaled on said second platen in mesh with said rack;   resilient means urging said stripper plate into contact with said first mold portion at the beginning of a mold-opening stroke; and   a link articulated at an eccentric location to said pinion and joined to said first platen by a lost-motion connection enabling limited separation of said stripper plate from said second mold portion whereby said stripper plate maintains contact with said first mold portion under the urging of said resilient means in an initial phase of said mold-opening stroke, said link coming into positive engagement with said stripper plate for breaking said contact at the end of said initial phase.   
     
     
       2. The combination defined in claim 1 wherein said resilient means comprises a spring anchored to said link and to a slider on said stripper plate guided in a slot of said link. 
     
     
       3. The combination defined in claim 1 or 2 wherein said eccentric location is so disposed on said pinion inwardly of the periphery thereof as to lie within an angle of less than 90° from the point of engagement of said pinion with said rack at the end of said initial phase whereby said link advances codirectionally with said rack, albeit at a lesser speed, during a further phase of said mold-opening stroke. 
     
     
       4. The combination defined in claim 3 wherein said lost-motion connection is dimensioned to establish said positive engagement in the second half of said mold-opening stroke. 
     
     
       5. The combination defined in claim 4 wherein the length of said mold-opening stroke is approximately half the circumference of said pinion, said eccentric location passing through a dead-center position near the end of said mold-opening stroke. 
     
     
       6. The combination defined in claim 1 or 2 wherein said pinion, said rack and said link are duplicated on opposite sides of said platens. 
     
     
       7. The combination defined in claim 1 wherein said platens include a third platen carrying a third mold portion confronting a fourth mold portion on a side of said second platen remote from said first platen; further comprising another rack in mesh with said pinion and secured to said third platen for displacing the latter symmetrically with said first platen relatively to said second platen, another stripper plate between said third and fourth mold portions penetrated by a core on said third mold portion, and another link articulated to said pinion at an eccentric location diametrically opposite the first-mentioned location, said other link being joined to said third platen by a lost-motion connection enabling limited separation of said other stripper plate from said second mold portion until the end of said initial phase whereupon said other link positively engages said other stripper plate for detaching the latter from said third mold portion, and other resilient means urging said other stripper plate into contact with said third mold portion in said initial phase. 
     
     
       8. The combination defined in claim 7 wherein said second platen is provided with injection means for feeding liquefied plastic material to cavities formed by said first and second mold portions and by said third and fourth mold portions. 
     
     
       9. The combination defined in claim 7 or 8 wherein said third platen is stationary and said first platen is provided with drive means for reciprocating same between said mold-closed and mold-open positions, with entrainment of said second platen by said racks and said pinion. 
     
     
       10. The combination defined in claim 7 or 8 wherein said stripper plates are provided with sliders guided in slots of the respective links, said resilient means comprising springs anchored to said links and to the associated sliders.